This application claims the benefit of German Patent Application 10118659.2 filed Apr. 14, 2001, herein incorporated by reference.
The present invention relates to a winding head of a textile machine.
It is known that considerable reductions of costs are possible, for example in preparation for fabric weaving, if the preset lengths of the yarn wound on the cheeses can be maintained as accurately as possible. This applies in particular when cheeses are placed together on a bank creel to be drawn off and warped or beamed. The greater the deviations in yarn length from one cheese to another, the greater the differences between the residual amounts of yarn left on the cheeses at the completion of the warp or beam. With high-quality yarn material, this problem leads to intolerable losses because of considerable amounts of wasted yarn, or to the necessity for elaborate and time-consuming re-winding of the residual yarn. In cheese-producing textile machines, it is customary to derive the length of yarn wound onto each cheese from the revolutions of the cheese or the revolutions of the drive roller for the cheeses during winding of the cheeses. Considerable inaccuracies in detecting the yarn length, or the yarn speed, can occur because of factors such as slippage or traversing motions.
Devices and methods are used for preventing such inaccuracies, by means of which the traveling yarn can be measured in a contactless manner, and signals which are proportional to the yarn speed can be generated. The speed which has been determined by means of a running time correlator, for example, can be evaluated for the determination of the length of the running time of a textile yarn.
For example, Swiss Patent Publication CH 669 777 A5 describes a method and a device for the contactless length measurement of a yarn wherein, by means of an optical correlation system having a screen and at least one photoelectrical detector, a yarn section is illuminated whose image is converted into an electrical push-pull signal containing a frequency proportional to the speed wherein, after separating push-pull portions and interference signals, the period length of the signal is respectively measured at least once during a scanning interval of a constant length of time if the signal exceeds a minimum amplitude value, and the length is determined from the individual measured length values, which were determined by forming the reciprocal value. A signal proportional to the yarn speed is generated in a contactless manner by the reproduction of a yarn section on a screen and photoelectrical conversion. The signal is scanned at fixed scanning intervals and the partial yarn length for each scanning interval is determined. The yarn length results from the addition of the partial lengths.
The method disclosed in German Patent Publication DE 43 27 587 A1 operates with a running time correlator. Here, the speed of the running yarn is measured at least at one reference winding location, a mean value is formed from this measurement and this mean value is used as the basis of the preset value of the winding speed at the remaining winding heads. By means of the direct detection of the winding speed at the running yarn, it is intended for the determination of the production output to reduce or eliminate the effects of interference factors, which heretofore have negatively affected the accuracy of the determination of the production output. The employment of such a measuring device for determining the winding speed of the running yarn only at one or a few winding heads of a cheese-producing textile machine is intended to provide a considerable savings in comparison to the arrangement of such measuring devices at all winding heads. However, using a few reference winding heads, or even only a single reference winding head out of a plurality of windings heads of the winding frame, it is not possible to assure that every cheese finished on this winding frame has a yarn length which matches with a sufficient accuracy the preset yarn length for use in the weaving preparation. The deviations from length between the detected, or determined produced amounts of yarn, which still occur even at reference winding heads, and the actual length of yarn wound on the cheese, are marginal in comparison to the production output and can therefore be easily neglected in the course of the determination of the production output of the entire winding frame. However, these deviations in length are no longer tolerable for the precise maintenance of a preset yarn length. Thus, a winding frame designed in accordance with German Patent Publication DE 43 27 587 A1 does not meet the greater demands made for agreement of the preset yarn length with the yarn length which is actually wound on the respective cheese.
As described in German Patent Publication DE 42 25 842 A1, European Patent Disclosure EP 0 000 721 A1 proposed to determine the yarn speed via two sensors disposed at a fixed distance from one another and operating in a contactless fashion. Sensors that operate optically or capacitatively, for instance, can be considered for this. These sensors detect stochastic yarn signals in the form of analog noise signals that result from irregularities in the yarn surface or yarn mass in the longitudinal direction of the yarn. The stochastic signal determined upstream in the yarn running direction is shifted temporally until it bears maximum similarity to the stochastic signal detected by the sensor disposed downstream. The thus-determined delay of the first signal corresponds to the time span required by the yarn to travel from the first to the second sensor. Because the spacing of the two sensors is known, the yarn speed can easily be determined in this manner. Typically, the mathematical operations typically characterized as cross-correlation methods are employed to achieve this; however, these calculations are time-consuming. The delay is not problematic when the yarn experiences no or only very little acceleration. However, rapid changes in speed, such as occur in the winding process after yarn breakage or bobbin changing, for instance, can not be controlled well enough in this manner to allow for precise measurement.
German Patent Publication DE 42 25 842 A1 incorporates and improves upon the running time correlator of European Patent Disclosure EP 0 000 721 A1. German Patent Publication DE 42 25 842 A1 shows a device for measuring the speed of textile yarns on a winding apparatus. The winding apparatus is used for producing cheeses, wherein the rotation of the cheese is created by means of the frictional effect from a drive roller. A running time correlator circuit such as the one described above with two measuring points, which are arranged at a fixed distance in the movement direction of the running textile yarn and where a contactless measurement is performed, and a further signal transmitter are connected with each other. The signal transmitter detects the rotary movement of the drive roller and emits signals which are proportional to the yarn speed. These signals are supplied to the running time correlator for presetting the range for latching of the control circuit to the correct maximum idle time (i.e., maximum of the correlation function for the running time of the yarn from the first to the second measuring point constitutes the idle time). As a result, it is possible to utilize the high degree of measuring accuracy of the running time correlator without a considerable outlay in computing capacity even at changing yarn speeds. The speed determined by means of the running time correlator can be directly evaluated via an integrator for the accumulated running time length determination of a textile yarn.
The publications cited above describe possibilities for precisely determining the yarn speed. However, the agreement of the yarn length wound on the cheese with the preset yarn length, as well as in a comparison of the cheeses with each other, still is insufficient for the greatest demands made on accuracy, in spite of a length measurement by means of the devices and methods described above.
It is accordingly an object of the present invention to improve the determination and storage of preset yarn lengths for cheeses.
This object is attained by providing a yarn winding head of a cheese-producing textile machine, with a device for accurately determining a cumulative length of yarn which has traveled through a yarn sensor, a device for determining a length portion of yarn removed in performing a yarn connecting process, and an evaluating device for calculating and storing a net yarn length wound onto a cheese at the winding head by subtracting the removed yarn length portion from the cumulative length of yarn which has traveled through the yarn sensor.
Thus, a winding head embodied in accordance with the invention is operative to subtract the partial lengths of removed yarn from the total cumulative length of the wound yarn derived from the yarn length which has traveled through the yarn sensor, whereby the calculated result determined in this manner is close to the actual value of the wound yarn length. This operation clearly increases the accuracy with which it is possible to maintain preset yarn lengths of cheeses, and leads to an improved utilization of the possibilities made available by a device for the most accurate determination of a yarn length passing through the yarn sensor.
In order to assure that it is possible, for example, to draw the required warp ends off a cheese in every case, it is customary under conventional practices to select the preset yarn length to be much greater than the yarn length actually required for the warping process. It is intended in this manner to provide for the possibility that, at the time the yarn length determined by conventional means of length measurement reaches the preset yarn length and the winding process is terminated, the yarn length actually wound on the cheese is less than the preset yarn length and is therefore not suitable for the desired use. While this customarily large amount of added yarn length is done for reasons of safety, the grave disadvantage thereby accepted is that large amounts of yarn are left on the bobbins as residual yarn, for example during the weaving preparation. Because of the clearly improved accuracy with which yarn lengths of a cheese can be maintained at a winding head embodied in accordance with the present invention, the additional yarn wound for safety can be kept very small in the process of presetting the yarn length, which leads to a significant reduction in the residual amounts of yarn left on the cheeses.
Preferably, the present device for the accurate determination of the length of the traveling yarn has a contactlessly operating measuring head with two measuring points, which are arranged in series with each other in the traveling direction of the yarn, as well as a running time correlator for processing the detected measured values. Advantageously, a particularly high accuracy can be achieved for the measurement of the yarn speed and the determination of the length of the running yarn.
It is also preferred that the running time correlator receives signals for presetting of the range for the correct latching on of the control circuit, which signals are generated by means of an angle sensor used for recording the circumferential speed of a drive roller for the cheese. In this manner, it is possible to react flexibly to speed changes, without a large computing effort and without a resultantly long computing time being required. Latching on to a secondary lobe, and therefore the generation of a false speed value, can be avoided.
The device for determining the lengths of removed yarn advantageously has a yarn end sensor arranged on an aspirating element which generates a start signal upon detecting the presence of a connecting end of yarn which was removed from the surface of the cheese by means of the aspirating element. The evaluation device is adapted to determine from the start signal and the signals from the angle sensor the yarn length unwound from the cheese for the yarn connecting operation. In this manner, the determination of the eliminated yarn length can be performed exactly.
The winding head preferably has means for yarn tensile strength control in the path of the yarn. Fluctuations in length of the wound-up yarn caused by variations in the yarn tensile strength are furthermore avoided to the greatest extent by means of such a yarn tensile strength control.
In a preferred embodiment, the evaluation device is embodied such that the determination of the yarn length for the length of yarn wound on the cheese takes place during the start-up of the winding device, at least in the initial phase of the start-up, exclusively on the basis of the signals generated by the angle sensor. A yarn length determination only on the basis of these signals can be terminated when a preset number of revolutions of the cheese is exceeded during the start-up, or a preset acceleration value in the rotary movement of the cheese falls below a set value. This arrangement avoids possible problems in the start-up phase of the rotation of the cheese which might be created because the relatively large time difference initially occurring between the signals from both measuring points causes the data volume which must be stored for the correlation to also be very large. Brief distortions of the determined length values possibly occurring during the relatively short start-up are minimal and can be tolerated, while the required computing outlay for the yarn length determination during the start-up is considerably reduced.
The device in accordance with the present invention makes it possible in a simple but effective way to achieve an extraordinarily precise agreement of the preset yarn length and the length of yarn actually wound onto the cheese. The invention now makes the accuracy of measurement of a correlation method with the aid of a running time correlator usable to the fullest extent in the course of the determination of the yarn length wound on a cheese.
Further details, features and advantages of the present invention will be described and understood in greater detail by the following disclosure of an exemplary embodiment represented in the accompanying drawings.